1. Field of the Invention
The present invention relates to a protection apparatus for an injection molding machine, which apparatus protects a movable mechanism including a movable member such as a screw.
2. Description of the Relevant Art
In general, an injection molding machine includes a movable mechanism such as a mold-clamping mechanism having a movable mold to be reciprocated within a predetermined stroke; and such a movable mechanism is provided with a protection apparatus (safety apparatus) for protecting an operator and the mechanism from accidents which would occur due to erroneous operation of the mechanism or an error in the operator""s work. In the technique disclosed in Japanese Patent Application Laid-Open (kokai) No. 10(1998)-296818, when a safety door of an injection molding machine is opened, this is detected by a limit switch, and a servomotor for driving a movable member is stopped immediately, whereby safety is secured during adjustment work or other types of work.
Meanwhile, in the measuring step of a molding cycle, a screw is rotated in order to move molten resin forward, and a predetermined back pressure is applied to the screw, whereby the molten resin is measured and accumulated in front of the screw. At this time, the screw retracts along the axial direction. However, the retraction speed of the screw is relatively low, and the screw is not a member which an operator touches directly or approaches. Therefore, conventionally, necessity for a protection apparatus as described above has been ignored.
However, when a controller for controlling a movable mechanism operates erroneously or breaks down, or when a temperature drift is generated due to long-term use or change in the surrounding environment, there arises a possibility that even when the screw has reached a measuring completion position, the controller judges that the screw has not yet reached the measuring completion position. In such a case, the screw continues its retraction and overruns, possibly causing breakage of the movable mechanism (injection mechanism); for example, breakage of a lock nut or a support bearing of a ball screw mechanism.
An object of the present invention is to provide a protection apparatus for an injection molding machine, which apparatus can reliably avoid overrun of a movable member and breakage of a movable mechanism due to overrun, even when a control system suffers erroneous operation or temperature drift.
Another object of the present invention is to provide a protection apparatus for an injection molding machine, which apparatus facilitates securing a space for installing the protection apparatus and a space for running wires, to thereby facilitate assembly and maintenance.
In order to achieve the objects as described above, a protection apparatus of the present invention comprises: an overrun detection mechanism including an element to be detected which is attached to one of a movable member of a movable mechanism and a stationary member facing the movable member, and a detection unit attached to the other of the movable member and the stationary member, the detection unit detecting the element when the movable member has moved to an overrun position; and a control section for forcedly stopping operation of a drive unit which moves the movable member, when the detection unit detects the element.
In a case in which a control system suffers erroneous operation or temperature drift and a movable member is on the verge of overrun during operation of the injection molding machine, when the movable member moves to the preset overrun position, the element is detected by the detection unit, so that the control section forcedly stops the operation of the drive unit which moves the movable member.